A blow molded container is obtained by performing a bottomed tubular preform with use of a thermoplastic resin material, and subsequently blow molding the preform. Since such a blow molded container has a high degree of flexibility in shape and is inexpensive, light in weight, and excellent in recyclability, the blow molded container is widely used as a container to be filled with a cosmetic product, a pharmaceutical product, a beverage product, or the like.
Generally, when a preform is blow molded in a blow mold, a trunk portion of the preform is accommodated in a blow mold, while a mouth portion as an orifice end of the preform is held by a holding jig from an inner wall side or an outer wall side of the mouth portion. Then, blow air is injected by means of the holding jig. Although sealing is established between the mouth portion of the preform and the holding jig so as to prevent leakage of the blow air, in order to allow the preform or a blow molded container to be detachable with respect to the holding jig, the mouth portion of the preform is loosely fitted to the holding jig. (Refer to Patent Literature 1 indicated below.) As a result, in correspondence with play between the mouth portion of the preform and the holding jig, there is a concern that the mouth portion might be deformed and enlarged in diameter due to a difference in pressure arising inside and outside the mouth portion when the blow air is injected.